Choosing the material for medical device
Medical device industry with its life impacting influences remains one of the most strictly regulated sectors. With critical aspects associated with medical, choice of material in medical devices has always been a challenging task for the designer and Engineer.
Product designers have to spend considerably much longer time in material selection for the medical device. In absence of right supporting data or guideline, this task becomes herculean. Many times failure of device largely originates from a wrong material selection. Almost 30-40% of FDA recall can be attributed to material failure 1. Designers and Engineers relying solely on material spec sheet often ignore the disclaimer given somewhere in corner or bottom of the page. ASTM tests (specified in Spec sheet) conducted on materials, are usually carried out in a controlled environment and may not be same as its actual usage conditions.
Many polymer manufacturers like DuPont maintain grades especially for medical application with more stringent control over manufacturing and quality 2. Large medical device industries employ large R&D teams comprising of experienced material scientists to help in this, but what about small enterprises or startups with innovative ideas. With my own past experiences, I have come up with few steps what would help to choose the right material.
All medical devices are regulated in different categories and classes based on the nature of use and risk involved in its usage. In vitro Devices (Devices that does not require direct contact with the patient) are categorized separately in classes mainly based on the risk associated. Many people underestimate the importance of these classifications and forget to check material compliance for medical use while development. These not only cause a change in design but the loss of time. So if your product falls in the high-risk category, any material you choose, make sure of its medical compliance.
FDA or CE guideline can be referred to classify device category 3, 4.
Mechanical, Thermal and Chemical characteristics of the material are very important like products, so do check for the spec sheet for properties and check its compatibility for specific conditions associated with usage.
Each component of the device will have its own unique set of requirement. While designing, ensure these requirements are covered. Maintain a list of conditions device will be exposed to. If any chemical reagents are used with the device, would be great to test a small piece of selected material with those chemical first.
Biocompatibility and Bio functionality of material is particularly critical for Medical device industry. Any adverse biological response with human contact to any components of the medical device is evaluated under the biocompatibility test. As implantable devices always remain in contact with body fluid, blood and tissue; its sensitivity and acceptability to host body remain of foremost importance. Biocompatibility assessment of material 5 apart from its physical and chemical parameters must also be evaluated as per ISO-10993 standard.
The manufacturing process of components also plays an important role as not all material fits all process. For very low volume production metal forming process like die casting or stamping can be very expensive and can easily be replaced with CNC machining. For plastic parts, Injection moulding can promise good finish and precision but need expensive tool development. Nowadays, advancement in additive manufacturing technology offers a variety of materials with high precision. While at the designing stage, make sure of the final manufacturing process to avoid redoing it again.
Device sterilization is something designers working in the non-medical field are not aware of and tend to usually ignore it while choosing the material. Sterilization requires device material resistance to sterilization method i.e. Autoclave, Gamma exposure, Ultrasonic cleaning or chemical sterilization. Identify if a device in development will have a sterile requirement or not, if yes, then what kind of sterile method will be used? So right at the beginning, you can be sure of material resistance to sterilization. Autoclave sterilization of plastic material may result in cracks or changed properties. Metal parts with continuous sterilization show some deformation.
Using a risk-based approach for material selection for each component of the device will also help in compliance with Regulatory requirements. Taking care of all these points, chances of material failure can be avoided significantly.
- Pandey E, Srivastava K, Gupta S, Srivastava S and Mishra N: Some Biocompatible Materials Used In Medical Practices- A Review. Int J Pharm Sci Res 2016; 7(7): 2748-55.doi: 10.13040/IJPSR.0975-8232.7(7).2748-55.
Blog By – Mukesh Malviya (Design Head)